Optical pickups record information on the surface of a disc, such as a compact disc, laser disc, video disc, or an optical magnetic disc, and read the information recorded on such a disc, by irradiating semiconductor laser light focused to a spot of several μm in diameter by a lens. Optical pickups are usually composed of optical elements, such as a light emitting element, a light receiving element, and a mirror, an optical frame which fixes these elements, an object lens, an object lens holder (hereinafter, simply referred to as a “lens holder”), an actuator member for tracking such parts to the movement of the optical disc, and a base frame which holds the actuator member and forms an optical path with the optical frame.
To advance weight and cost reduction of optical pickups, attempts are being made to switch the component materials from metal to resin. Even among thermoplastic resins, attention has especially been paid to liquid crystal polyester resins for optical pickup components, such as lens holders and base frames, due to their excellent mechanical properties, moldability, dimensional accuracy, heat resistance, and damping properties. However, with the increasing volume and recording/reading speed of information handled by recent digital disc drive apparatuses, the requirements for the damping properties have become stricter. In addition, high performance properties are also now required even for the liquid crystal polyester resin compositions forming the components of the optical pickup.
Especially for recent DVD and Blu-ray devices, the requirements have become stricter. For DVD high-speed recording systems, the resin components need to have a specific gravity of 1.4 to 1.5. Especially for the short pickups mounted in notebook computers, high damping properties with an even higher resonant frequency and loss coefficient, and an excellent balance between these, are required. For Blu-ray recording systems, a specific gravity of 1.3 or less is preferred, while for playback systems, a specific gravity of 1.5 or less is preferred, and high resonant frequency and high loss coefficient are desired. Specifically, when the resonant frequency is 2500 Hz or more, the loss coefficient is preferably 0.15 or more.
Conventionally, there have been several proposals for liquid crystal polyester resin compositions suited for a component forming an optical pickup. For example, a resin composition has been proposed which has 100 parts by weight of liquid crystal polyester and 5 to 20 parts by weight of glass fibers which have a post-molding number average fiber diameter of 2 to 20 μm and a post-molding number average fiber length of 210 to 500 μm (see Patent Document 1). Another example which has been proposed is a resin composition which includes 100 parts by weight of wholly aromatic liquid crystal polyester, which has a melting point of 400° C. or more or a liquid crystal starting temperature in which the apparent viscosity at a temperature 20° C. above of this temperature is 1000 poise or more, and 5 to 100 parts by weight of glass fibers which have a number average fiber length of 50 to 200 μm (see Patent Document 2). However, with these resin compositions, a resin having low specific gravity and high damping properties cannot be obtained, and thus these resin compositions cannot meet the requirements for short type pickups for use in high-speed DVD systems and playback pickups for use in Blu-ray systems.    Patent Document 1: Japanese Patent Application Laid-Open No. 2001-288342    Patent Document 2: Japanese Patent Application Laid-Open No. 2005-89652